This invention generally relates to endless track driven vehicles such a snowmobiles and more particularly to means associated with the suspension system of the vehicle for maintaining the endless driving track under substantially uniform tension and track length.
Variations in track tension and/or track length detrimentally effect several operating conditions of the endless track. One undesirable result is in relation to rolling resistance, that is resistance between idle and drive wheels engaged with the endless track and also resistance between the track and the ground surface. Variations in track tension effect the power transmitted to the endless track and also the power transmitted from the endless track to propel the vehicle. Another undesirable effect is that track life is shortened or decreased because of continual stressing of the track material causing uneven or undue wear and fatigue. Variation in track tension is also related to suspension compliance in that movement of the suspension system is responded to by a varying stress on the endless track. It is, therefore, desirable that an endless track for a track driven type vehicle be maintained at a substantially uniform constant tension under varying conditions of loading, terrain and operation in order to optimize the performance of the track driven vehicle.
It will be understood that endless track vehicles may be provided with different suspension system in which the attempt to maintain uniform track tension is sought by variough systems. For example, in U.S. Pat. No. 3,863,727, an endless track passes around two spaced fixed axes and the bottom lay of the track is biased away from the plane of the fixed axes by pneumatic springs. In this system , the track does not flex at the lower ground engaging lay.
In U.S. Pat. No. 3,362,492 bogey wheels are provided between top and bottom lays of an endless track to maintain pressure against the lower lay of the track. In U.S. Pat. No. 3,610,356 the top surface of the upper lay of an endless track is engaged by a tension roller.
In U.S. Pat. No. 3,705,637 tension on an endless track is controlled by torsion springs mounted on members of the suspension system, the torsion springs being connected to a frame which carries idle wheels which exert a downward pressure against the bottom lay of the track.
In such prior proposed endless track systems, the travel of the suspension systems are relatively limited and the pressure against one of the lays of the endless track is maintained by a separate pressure biasing system which is usually not related to movement of the suspension system.
Changes in variation of length of track results in noticeable changes in track tension in terms of pounds and thereby directly effects operating characteristics of the track vehicle and maintenance of the endless track.